Cecil Family, originally also spelled Sitsilt, Syssell, or Seisill, one of England’s most famous and politically influential families, represented by two branches, holding respectively the marquessates of Exeter and Salisbury, both descended from William Cecil, Lord Burghley, Elizabeth I’s lord treasurer. Burghley’s elder son, Thomas, was created Earl of Exeter, and his descendant the 10th Earl was made a marquess in 1801. This line has remained seated at Burghley House in Northamptonshire, the great mansion built by Lord Burghley. Burghley’s second son, Robert, created Earl of Salisbury in 1605, built a new house at Hatfield, the seat of his descendants the earls (later marquesses) of Salisbury, who in the 19th and 20th centuries were prominently connected with the British Conservative Party.